The present invention relates first to an electric field sensor or an electro-magnetic wave sensor using liquid crystal, and then a line sensor and an image sensor using a linear and two-dimensional array of such sensors. The same construction of the liquid crystal of a microscopic size can also function as an optical modulator. So the present invention further relates to a movie player/recorder using such liquid crystal as an image sensor and as an optical modulator.
A liquid crystal cell is in many cases used as an actuator to pass or stop light, and especially as a display with a segment structure or with a fine two-dimensional cell array structure. In some cases, it is also used as a sensor. As a sensor, it is mostly used as a temperature sensor utilizing the characteristic change due to the temperature change or an electric field/magnetic field sensor utilizing the characteristic change due to the change in the temperature and the electro-magnetic field combined.
In the Publication No. H6-289399 of the Japanese Patent Application, a liquid crystal cell sensitive to the change in the magnetic field is disclosed. The liquid crystal cell is made of ferroelectric liquid crystal contained in two outer plates, each of which is made of a transparent base plate, a transparent electrode layer, and an alignment layer. The alignment layer is placed inside of the cell, and at least one of the alignment layer is photo-excitable (i.e., can be excited by a photon-irradiation). When the liquid crystal cell is slowly cooled from the isotropic temperature while a DC (direct current) voltage larger than a certain threshold value is applied between the electrode layers, the spontaneous polarizing direction of the ferroelectric liquid crystal molecules uniformly aligns. Then, a DC voltage of the opposite direction to the previous one having the magnitude below the threshold value is applied to the liquid crystal cell. When, under such a reverse-biased condition, a light beam is spotted on a preferred place, the photo-excitable plastic in the alignment layer of the spotted area is excited, and the polarizing direction of the ferroelectric liquid crystal molecules adjacent to the alignment layer is reversed. Since, as a result, the direction of the long liquid crystal molecules differs between those in the light-spotted area and those in the unspotted area, data can be recorded using the dark part in the unspotted area and the bright part with an oblique liquid crystal molecules in the light spotted area by properly setting the Cross-Nicol liquid crystal angle.
In the JPA Publication No. H10-222045, a three-dimensional color movie recorder/player is disclosed. In the recorder/player, pulse lasers of three primary colors are used, and the interference image of the object light and the reference light is formed in a time-splitting manner for every color. The interference images are recorded by photoelectric image sensor. A color movie is reproduced in the same time-splitting manner from the recorded data using similar pulse lasers of the three primary colors.
In the JPA Publication No. H11-006983, a movie playing method using a variable diffraction grating is disclosed. In the variable diffraction grating, the diffracting condition of light gradually changes from line to line. A movie is reproduced by moving the variable diffraction grating according to the data of the movie.
In the liquid crystal cell disclosed in the JPA Publication No. H6-289399, the ferroelectric liquid crystal is heated above the isotropic temperature and a DC voltage larger than a certain critical value is applied so that the ferroelectric liquid crystal molecules align according to the direction of the applied voltage. When the liquid crystal is cooled below the isotropic temperature, the alignment of the ferroelectric liquid crystal molecules is frozen. When in such a state a light beam is spotted on the liquid crystal, the alignment of the liquid crystal molecules changes in the spotted area, whereby data is recorded. In summary, the liquid crystal cell disclosed in the JPA Publication No. H6-289399 is a recording device and may not be used as a sensor for detecting a dynamically changing electric field.
In the first feature of the present invention, an electric field sensor of a liquid crystal cell is provided. The inventive sensor is applicable, as easily understood, to an electro-magnetic sensor, a line sensor, an image sensor, etc.
In the inventive electric field sensor, an electric field is detected as follows. Liquid crystal is filled between a pair of parallel plate electrodes, and a DC voltage is applied between the pair of plate electrodes for the molecules of the liquid crystal to align perpendicular to the plane of the plate electrodes. When an electric field having a component parallel to the plane of the plate electrodes is applied, a deviation from the alignment of the liquid crystal molecules occurs. The deviation of the alignment is detected by a change in the capacitance or a change in the electric resistance between the pair of plate electrodes, whereby the electric field is detected by the liquid crystal cell.
Since a liquid crystal molecule 11 is an electrically polarized long molecule, the liquid crystal molecules 11 align, as shown in FIG. 1A, perpendicular to the plate electrodes 12 and 13 when a DC voltage is applied between the plate electrodes 12 and 13. When another electric field is applied oblique to that produced by the pair of plate electrodes 12 and 13, the alignment of the liquid crystal molecules 11 deviates from the normal position as shown in FIG. 1B. When the alignment of the liquid crystal molecules 11 deviates from the normal position, the capacitance and the electric resistance between the pair of plate electrodes 12 and 13 change. By detecting either one of the physical properties using an appropriate known circuit including the plate electrodes 12 and 13, the change in the externally applied electric field is detected.
The time (recovery time) necessary for the liquid crystal molecules 11 to return to the normal (original) state perpendicular to the plate electrodes 12 and 13 from the deviated state depends on the physical properties of the liquid crystal and the magnitude of the DC voltage applied between the plate electrodes 12 and 13. By using liquid crystal having adequately short recovery time (or having adequately high responsibility) and by applying an adequately high DC voltage between the plate electrodes 12 and 13, a high-speed electric field sensor that can respond to a high-speed change in the electric field can be made. Since the electro-magnetic wave is a transverse wave in which the electric field oscillates perpendicular to the propagating direction of the electro-magnetic wave, the inventive electric field sensor may be used as an electro-magnetic wave sensor for detecting the wave propagating perpendicular (or nearly perpendicular) to the plane of the plate electrodes 12 and 13.
As the frequency of the electro-magnetic wave becomes higher, it becomes more difficult for the liquid crystal molecules to follow the changing speed of the electric field. In this case, the detecting method may be changed so that the vibration of the liquid crystal molecules due to the electro-magnetic wave is detected by the change in the capacitance or the electric resistance between the plate electrodes.
Since infrared and visible lights are included in the electro-magnetic wave, the above described inventive electro-magnetic wave sensor may be used as a photo-sensor (including an infrared sensor). In this case, transparent electrodes such as using ITO (Indium Tin Oxide) should be used.
By arraying small cells of such liquid crystal electro-magnetic wave sensor as described above in a row, a line sensor is made, and by arraying such small cells two-dimensionally, an image sensor is obtained. Since every cell can be made of a dynamic (or high-speed) electro-magnetic wave sensor cell, the line sensor and the image sensor can be used as a dynamic sensor (movie sensor).
As for recording and playing of a three dimensional movie, the method disclosed in the JPA Publication No. H10-222045 uses, on one hand, a normal photo-electric image sensor for recording an interference pattern. The method uses, on the other hand, a liquid crystal panel in playing the recorded interference pattern to reproduce a color movie. That is, the method uses two different devices in recording and in playing, which requires a complicated total system and hence a subtle matching adjustment between the recording device and the playing device is necessitated.
In the second feature of the present invention, a single and simple system using a two-dimensional array of the above cited liquid crystal cells is provided for recording and playing a three dimensional movie by itself. A two-dimensional array of liquid crystal cells of a microscopic size can be used as a dynamic valuable non-mechanical optical modulator.
That is, an interference pattern is recorded by a liquid crystal panel of the above-described image sensor of the present invention, and the same liquid crystal panel is also used as an optical modulator for playing the interference pattern to reproduce the recorded three-dimensional movie. Thus the inventive system first includes a liquid crystal panel which is composed of a two-dimensional array of small cells functioning as an image sensor. On the inner faces of the pair of plate electrodes constituting the liquid crystal panel are provided alignment layers having the same aligning direction. The system also includes a coherent light source for generating a coherent light, a light splitter for splitting the light from the coherent light source into two beams, and a recorder for recording an image data of the interference pattern sent out from the image sensor.
A three-dimensional movie is recorded in the system as follows. The coherent light from the light source is split into two beams, and one of which is irradiated onto an object and the other is irradiated onto the liquid crystal panel image sensor as a reference light. A part of the light irradiated onto the object is reflected by the object and comes to the image sensor as an object light. The object light is superposed on the reference light on the liquid crystal panel image sensor and generates an interference pattern on it. The interference pattern includes the information of the three dimensional shape of the object. The interference pattern is detected by the image sensor and the data of the interference pattern is recorded in the recorder. Thus the three dimensional image is recorded in the inventive system. Since the liquid crystal panel image sensor of the present invention can detect a moving image, a three-dimensional movie can be recorded by concurrently recording the continuously changing interference pattern.
Reproduction of the three-dimensional movie is achieved almost in the reverse direction of the above process, as follows. The recorded interference pattern is continuously played on the liquid crystal panel (which was used as an image sensor in the recording mode) while the reference light is cast onto the liquid crystal panel, whereby a viewer of the liquid crystal panel perceives a three-dimensional movie.
It is possible to construct a color version of the above-described three-dimensional movie recording/playing system. In the three-dimensional color movie system, three coherent light sources for the three primary colors and a light chopper is provided besides the elements used in the above monochromatic system.
In recording, the chopper allows one of the three primary color light from the three light sources pass at a time, and allows the next color light pass the next moment. Thus the light chopper switches the three primary color coherent lights one from another cyclically at a high speed. Every primary color passing the light chopper generates an interference pattern on the liquid crystal panel as described above and the interference pattern of the color of the moment is recorded in the recorder. Thus a three-dimensional color movie is recorded.
In playing, the light chopper is controlled to synchronize with the timing of recording so that every picture of the moment is reproduced from the interference pattern using the reference light of the appropriate color. Continuous reproduction of such pictures gives the viewer the perception of a three-dimensional color movie.
As a sensor, the liquid crystal panel with microscopic sized cells is used not only for recording a three-dimensional movie, but also for various optical devices, for example, an optical memory with very high density, or a real-time observation device of a microscopic image, etc.
As a dynamic valuable non-mechanical optical modulator, the liquid crystal panel with microscopic sized cells can be used in broader applications, such as for optical fibers, photonic bandgap structures or nonlinear optical materials.
Thus the microscopic liquid crystal panel may be one of the basic optical technologies in the future.